A power supply reverse connection protection function that prevents, in a case where a plus terminal and a minus terminal of an in-vehicle battery are connected reversely, a failure of in-vehicle equipment due to a current flow in a direction opposite to that in a normally connected case is proposed in, e.g., each of Patent Documents 1 and 2.
In a power supply reverse connection protection circuit according to Patent Document 1, on a power supply wiring that connects a power supply terminal connected to a plus terminal of a battery and a control circuit as a power supply target, an N-channel first FET (field-effect transistor) is provided such that an anode of a parasitic diode of the first FET is situated at the side of the power supply terminal, and an N-channel second FET is further provided on the downstream side of the first FET such that a cathode of a parasitic diode of the second FET is situated at the side of the first FET. During reverse connection of the battery, the first FET and the second FET are turned off, and a reverse current is inhibited by the parasitic diode of the first FET.
As a generation method of operation power for each gate of the first FET and the second FET in the conventional power supply reverse connection protection circuit, a method in which a charge pump-type booster circuit is provided in parallel with a feeder circuit that supplies power from the battery to the power supply target, and power from the booster circuit is applied to the gates has been mainly used (see, e.g., Patent Document 1).
Since the charge pump-type booster circuit requires many components such as a capacitor for boosting switching, a capacitor for smoothing, a plurality of switching elements for controlling charging and discharging of the capacitor for boosting switching, and a control circuit for switching between ON and OFF of the switching elements, the booster circuit becomes a factor responsible for an increase in size of a device and an increase in cost.
In order to avoid the increase in size of the device, an IC (Integrated Circuit) dedicated for the charge pump in which the above functions are integrated into one package or a high-function FET in which the charge pump-type booster circuit is included in the FET is developed. However, these devices serve as means for avoiding the increase in size of the device, but the increase in cost cannot be avoided.
In addition, Patent Document 2 discloses a power supply reverse connection protection circuit that uses two N-channel FETs, but the detail of a gate driver power generation circuit that generates the operation power for the FET is not described.
On the other hand, in Patent Document 3, a configuration in which multiple voltages are used and the charge pump circuit is not used is proposed. A power supply device according to Patent Document 3 includes a 12 V power supply and a 36 V power supply, and power supply from the 12 V power supply to a load is controlled by applying power from the 36 V power supply to the gate of an N-channel FET to thus turn on the FET. This method is presupposed to use multiple voltages of the power supply.